Product and process using novel binder means for non-woven fabrics



P 15, 1964 R. M. HOFFMAN ETAL 3,148,999

PRODUCT AND PROCESS usmc NOVEL BINDER MEANS FOR NON-WOVEN FABRICS Filed July 18, 1962 INV EN TOR5 BY MWA United States Patent 3,148,999 PRODUCT AND PROCESS USING NOVEL BINDER MEANS FOR NON-WOVEN FABRICS Robert Michael Hoffman and Robert Preyer Motfett, Wilmington, Deh, assignors to E. I. du Pont tie Nernours and Company, Wilmington, Del., a corporation of Delaware Filed July 18, 1962, Ser. No. 210,721 3 Qlaims. (Cl. 117-4) This invention relates to novel binder fibers for nonwoven fabrics and more particularly to novel binder fibers for non-woven fabrics that achieve uniform internal distribution of binder particles or bonds throughout the nonwoven fabrics.

It is an object of this invention to provide a novel form of binder material for non-woven fabrics. It is a further object to provide a binder material for non-woven fabrics which will permit the generation of regularly distributed, uniformly spaced bond points within and throughout the non-woven fabric. It is a still further object to provide non-woven fabrics bonded with such binder material. Other objects will become apparent in the course of the following specification and claims.

In accordance with this invention, the objects are achieved by a staple fiber of a relatively insensitive synthetic polymer having adhered thereto a single globule of a second synthetic polymer having a diameter of about to times the diameter of the staple fiber and having a melting point less than said staple fiber.

These beaded fibers can be made by any of several processes. In one process a solution of the lower melting polymer is applied at fixed intervals to a moving web of continuous fibers of relatively thermally insensitive synthetic polymer. After the globules are applied, they are dried by heat and then cut to 1 /2 to 3 inch staple fibers. In another process, continuous filaments of the lower melting copolymer are draped over a stationary web of fibers of relatively thermally insensitive synthetic polymer at predetermined intervals and the entire web is subjected to a temperature above the melting point of said copolymer. This temperature causes the low melting copolymer filaments to melt and flow to their crossover points on the Warp filament where they form globules. In a preferred embodiment of this invention is a process which comprises intimately contacting fibers of synthetic organic polymer at predetermined intervals of about 1 /2 to 3 inches with a solution of synthetic organic polymer from the class consisting of polyarnides and copolyamides and having a melting point less than said staple fibers, drying said synthetic polymer as globules onto said staple fibers at said predetermined intervals and cutting said staple fibers into staple of about 1 /2 to 3 inches in length.

The globules of binder polymer must be large in diameter compared to the staple fiber diameter and preferably between 10 and 30 times the diameter of the staple fiber. The globules of binder polymer are preferably spaced on the average no closer together along any continuous filament than the length of the average staple fiber after being processed into staple, so that on the average only one globule of binder polymer is attached to any single staple binder fiber that has been processed into staple.

When non-woven fabrics are prepared from such fibers, the beaded binder fibers are preferably blended with nonbinder fibers in such proportion that one globule occurs approximately every 15-25 inches of total length of the mixed fiber material in the fabric.

In the attached drawing there are graphic illustrations of certain embodiments of this invention. FIGURE 1 represents a longitudinal view of one novel beaded fiber after being processed into staple. FIGURE 2 represents 3,148,999 Patented Sept. 15., 1964- "Ice a longitudinal view of beaded fibers intermeshed with non-beaded fibers prior to processing into a non-woven fabric. FIGURE 3 represents a longitudinal view of these novel beaded fibers prior to processing into staple.

In FIGURES 1, 2 and 3, 1 represents the staple fiber of relatively thermally insensitive material, 2 represents the adhering globule of lower melting binder polymer spaced at predetermined intervals along the staple fiber. In FIGURE 2, 3 represents the non-beaded staple fibers prior to processing into non-woven fabrics.

To indicate more fully the nature of the present invention, the following examples of typical procedures are set forth, it being understood that these examples are presented by way of illustration only, and not as limiting the scope of the invention.

Example I A warp of three denier per filament nylon multi-filaments of polyhexamethylene adipamide (66) separated from each other by a distance of /8 inch, is strung up on a frame. Approximately 20 denier per filament copolyamide monofilaments are then laced across the warp at 1 /2 inch intervals. The copolyamide is composed of a blend of 30% of polyhexamethylene adipamide and 70% polyhexamethylene sebacamide. The frame containing the warp and filling filaments is placed in an oven at between 200 and 205 C. for approximately 10 minutes. This treatment causes the low melting copolyamide filaments to melt and flow to their crossover points on the warp filament where they form globules of from 10 to 30 times the diameter of the warp filament. After removal of the frame from the oven, the warp filaments are then cut to 1 /2 inch staple fibers, each containing one globule of polymer binder. Other predetermined intervals of placing the globules along the staple fiber can be used to permit the type structure desired of the nonwoven fabric made therefrom.

Example 11 5 minutes. Upon removal of the frame from the oven,

globules of from 10 to 30 times the diameter of the warp filaments are observed as in Example I. The filaments are then cut to staple lengths 1 /2 inches. Other predetermined intervals of placing the globules along the staple fiber can be used to permit the type structure desired of the non-Woven fabric made therefrom.

Example III In an embodiment of the preferred process of this invention a warp sheet of nylon monofilaments is prepared for continuous application'of binder globules. The warp of filaments is strung up and run across a binder applicator roller and rewound on a second warp beam. The binder applicator roller consists of a cylindrical plastic roller with a diameter of 1 inch, corresponding to a circumference of approximately 3.14 inches. A groove is cut along the surface of this roller, parallel to the axis and extending the full length of the roller. The groove is inch wide and & inch deep. The roller is placed so that it revolves with the lower quarter of its surface immersed in a solution of polyamide resin in ethyl alcohol as described in Example II. The top surface of the roll is adjusted so that it is in touching contact with the warp sheet as the latter is unwound and rewound. The binder applicator roll is positively geared to operate at the same speed as the windup roll, thus permitting the application of droplets of binder solution along the length of each of the filaments as described in Example I composing the warp sheet, at approximately 3 inch intervals. After the binder globules has been applied, and before they reach the windup roll, they are dried by the application of infra-red heat from a bank of infra-red lamps situated above the warp sheet. The diameter of these globules are from 10 to 30 times the diameter of the warp filaments as described in Example I. These lamps remove the solvent from the beads and permit the Winding up of a dry, continuous filament warp of binder fibers, which are then available for cutting into binder staple as described in Example I. Other predetermined intervals of placing the globules along the staple fiber can be used to permit the type structure desired of the non-woven fabric made therefrom.

Example IV A non-woven fabric is prepared from beaded binder fibers made as described in Example III as follows. The beaded fibers are distributed by hand among four layers of a oz./yd. web of 3 d.p.f., 1 /2 inch staple nylon fibers. The binder concentration of beaded staple fibers in the web is approximately 5% to 25% with approximately preferred. The web containing beaded fiber binder is pressed at 375 F. and 50 lbs/in. for one minute. Temperatures at which the staple fibers will melt are avoided. The sample is dyed, brushed, sheared and pressed. The resulting fabric is identical in appearance to a control fabric bonded with granular polyamide resin of the same type.

The staple fibers of relatively thermally insensitive material useful in preparing the beaded staple of the present invention can consist of synthetic linear polyamides such as polyhexamethylene adipamide, polyhexamethylene sebacamide, polycaproamide and interpolyamides; and polyesters, and polyesteramides, and mixtures or blends thereof such as dibasic diamide or amino acid polyamides, dibasic dihydroxy acid/polyester. Other fibers which can be used, preferably as mixtures with fibers of the polyamide, polyester or polyesteramide types, include cotton, ramie, viscose rayon, acetate rayon, wool, polyacrylonitrile, acrylonitrile copolymers, polyurethanes and polyvinyl acetals.

The globules of lower melting binder can consist of various copolymers that have lower melting points than the staple fiber with polyamide resins and copolyam-ide resins such as polyhexamethylene adipamide/polycaproamides (66/6) and polyhexamethylene adipamide/polyhexamethylene sebacamide/polycaproamide (66/ 610/ 6 being preferred.

While the preceding examples have described the use of polyarnide binder and polyamide fiber it is equally possible to employ other staple fibers of relatively insensitive material in conjunction with binder material, such as polyester fibers and binder material, acrylic fibers and binder material or other similar synthetic thermoplastic polymeric material as the binder component and other fibers such as mixtures of the above fibers, and the above fibers mixed with cotton, ramie, viscose rayon, acetate rayon, wool, polyacrylonitrile, acrylonitrile copolymers,

polyurethanes and polyvinyl acetals as the non-woven fabric-forming material. In addition, other alternate combinations of the above ingredients are also possible.

By using binder fibers of the type described, difficulties with distribuiton and retention of granular particles in the web are solved. In addition, the straightfiber portion of the binder fiber facilitates distribution in both carding and air deposition machines, and serves to anchor the binder globule in the web prior to activation of the binder globule by the application of heat and pressure. Moreover, by controlling the size of the bead andthe spacing of the beads onto the staple fiber, bonding may be carried out employing any preferred geometrical arrangement, leading to superior fabrics. Furthermore, use of binder in the manner described permits maximum utilization and efiiciency of binder material with no unused binder remaining in the fabric.

The above-described principles of beaded binder fibers are simple but their advantages are manifold. As already described, distribution of binder material is more easily effected and is more uniform. Closer spacing of binder globules permits a stiffer, more rigid structure. Longer staple fibers with more remotely spaced binder globules permits softer looser structures to be made. It is the important aspect of this invention that such qualities can be controlled exactly, precisely and reproducibly without recourse to elaborate or complicated binder procedures.

Many equivalent modifications will be apparent to those skilled in the art from a reading of the above without a departure from the inventive concept.

What is claimed is:

1. A staple fiber of a synthetic organic polymer having attached thereto a single globule of a synthetic organic polymer having a diameter of about 10 to 30 times the diameter of the staple fiber and having a melting point less than said staple fiber.

2. An unbonded assembly of staple fibers, at least about 10% of which are staple fibers of a synthetic organic polymer each having attached thereto a single globule of a synthetic organic polymer having a diameter of about 10 to 30 times the diameter of the staple fiber and having a melting point less than said staple fiber.

3. A process which comprises intimately contacting filaments of synthetic organic polymer at predetermined intervals of about 1 /2 to 3 inches with a solution of synthetic organic polymer from the class consisting of polyamides and copolyamides and having a melting point less than said filaments, drying said synthetic polymer as globules onto said filaments at said predetermined inter- Vals and cutting said filaments into staple of about 1 /2 to 3 inches in length.

References Cited in the file of this patent UNITED STATES PATENTS 2,424,743 Davis July 29, 1947 2,844,491 Hubbard July 22, 1958 2,880,112 Drelich Mar. 31, 1959 3,087,833 Drelich Apr. 30, 1963 FOREIGN PATENTS 791,618 Great Britain Mar. 5, 1958 

1. A STAPLE FIBER OF A SYNTHETIC ORGANIC POLYMER HAVING ATTACHED THERETO A SINGLE GLOBULE OF A SYNTHETIC ORGANIC POLYMER HAVING A DIAMETER OF ABOUT 10 TO 30 TIMES THE DIAMETER OF THE STAPLE FIBER AND HAVING A MELTING POINT LESS THAN SAID STAPLE FIBER. 